Experimental Study On The Effect Of Impact Loadings On Stress Wave Propagation Characteristics Of Rock Under Geostress

During blasting and the excavation of underground rock mass engineering,due to the redistribution of geo-stress and the attenuation mechanism of stress wave propagation,the engineering rock mass at different distances from the blast source bears different magnitudes of geo-stress and impact load.Different magnitudes of geo-stress lead to different compaction and damage degrees of surrounding rock mass,thus changing its stress wave propagation attenuation characteristics.Due to the attenuation of the stress wave,the surrounding rock in different parts is subjected to different degrees of dynamic impact load,thus showing different stress wave propagation characteristics.In order to study the effect of impact load and geostress on the propagation characteristics of stress wave in rock,a modified Split Hopkinson Pressure Bar(SHPB)system was used to carry out stress wave propagation test on red sandstone.Five grades of static stress and impact velocity are set respectively to simulate different geo-stresses and impact loads on rocks in actual engineering.The influence characteristics of impact velocity and three-dimensional static stress on stress wave waveform,amplitude characteristics,transmission coefficient of stress wave,propagation velocity of stress wave in red sandstone and acoustic wave velocity of rock after impact are analyzed.The main contents and conclusions are as follows:(1)Based on the stress wave waveform data obtained from the test,the influence of impact load and geostress on the stress wave waveform and attenuation characteristics was explored.The results show that when the confining pressure on the rock remains unchanged,the strain value corresponding to the transition section(the stress wave band between the incident wave and the reflected wave)increases with the increase of the axial static stress at the same impact velocity.Under the action of the same three-dimensional static stress,with the increase of the impact velocity,the amplitude of the incident wave and the reflected wave both increase linearly;the amplitude of the transmitted wave increases nonlinearly with the increase of the impact velocity.large,and the rate of increase is getting smaller and smaller.When the impact velocity is similar,the amplitude of the incident wave signal decreases linearly with the increase of the axial static stress;the reflected wave amplitude increases with the increase of the axial static stress.When the three-dimensional static stress is constant,the stress wave transmission coefficient decreases with the increase of the impact velocity;when the impact velocity is similar and the confining pressure is constant,the stress wave transmission coefficient first increases and then decreases with the increase of the axial static stress.(2)Based on the stress wave waveform test data obtained from the stress wave propagation test,by determining the time difference between the take-off point and the amplitude point of the incident wave and the transmitted wave,the stress wave propagation velocity and the amplitude point of the rock stress wave take-off point are calculated.transmission speed.The influence characteristics of impact velocity on rock stress wave propagation velocity are analyzed and compared with the variation law of rock acoustic wave velocity after loading.The results show that under the same three-dimensional static stress conditions,the stress wave propagation velocity at the starting point of the stress wave is greater than that at the amplitude point.When the three-dimensional static stress of the rock specimen is small,the propagation velocity of the stress wave at the take-off point and the propagation velocity of the amplitude point increase with the increase of the impact velocity;when the three-dimensional static stress of the rock specimen is large,the take-off point The propagation velocity of the stress wave and the propagation velocity of the amplitude point first increase and then decrease with the increase of the impact velocity.The acoustic wave velocity of the loaded rock decreases linearly with the increase of the impact velocity.(3)Based on the relationship between stress wave propagation velocity and impact velocity,the empirical model of stress wave propagation velocity changing with impact velocity was obtained.By observing the influence of fitting parameters on the fitting curve,the physical and mechanical significance of fitting parameters was determined,and the influence of axial static stress on each parameter was analyzed.The results show that when the confining pressure is constant,with the increase of axial static stress,the minimum stress velocity in the model of stress wave velocity and impact velocity at the jump point increases nonlinearly,and the increase amplitude becomes smaller and smaller.The critical impact velocity increases first and then decreases,and the stress wave velocity sensitive factor increases first and then decreases.With the increase of axial static stress,the minimum stress velocity in the model of stress wave velocity and impact velocity at the amplitude point increases nonlinearly,while the sensitive factor of critical impact velocity and stress wave velocity decreases all the time.